In lichenoid drug reactions the pathology is nearly identical to lichen planus. There is a dense, band-like lymphocyticinfiltrate in dermis that obscures dermoepidermal junction, cytoplasmic vacuolisation of basalkeratinocytes and apoptotic keratinocytes that degenerate into colloid bodies (figures 1,2). In addition, there are usually eosinophils in the infiltrate (best seen in figure 3).
Differential diagnosis for lichenoid drug eruption
Other diagnoses to be considered include any lichenoid dermatosis. The key differential is lichen planus. Clinical correlation can be very useful. Key histologic features seen in lichenoid drug eruptions, that are not common in idiopathic lichen planus, include the presence of eosinophils and the presence of prominent parakeratosis.